Steam-engine relief-valve



(No Model.)

JJH. DUIFEY. STEAM ENGINE RELIEF VALVE.

No. 333,616. Patented Jan. 5,188.6.

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UNITED STATES PATENT OFFICE.

JAMES HENRY DUFFEY, OF ST. PAUL, MINNESOTA.

STEAM-ENGINE RELIEF-VALVE.

BPECIECATION forming part of Letters Patent No. 333,616, dated January 5, 1886. Application led October 5, 1855. Serial No. 179,086. (No modehl To all whom it may concern:

Be it known that l, JAMES HENRY DUEFEY, acitizen of the United States7 and residing at St. Paul, in the county of Ramsey and State of Minnesota, have invented certain new and useful Improvements in Steam-Engine Relief- Valves, of which the following is a specification.

Thisinvention relates to steam-engines; and it consists in the arrangement ofthe valves by which steam is admitted tothe cylinder, whereby the formation of back-pressure in the exhaust end of the cylinderis prevented and the expansive power ofthe steam used to a much greater degree, as hereinafter shown and described.

This invention maybe applied to nearly all forms of engines; but for the purpose of illustration I have shown it in the drawings applied to an ordinary engine, the slide-valve of which is modied to adapt it to my invention.

In the drawings, Figure l represents a side view of the cylinder and steam-chest, the latter being in section, and a cross-sectional view of the driving-shaft with the two eccentrics in outline thereon. Fig. 2 is a sectional View through the cylinder and steam-chest, showing the position ofthe valves when the piston-head is at the extreme right end of its stroke. Fig. 3 is a cross-sectional view of Fig. 2 on a line through the exhaust port and valves. Fig. 4 is a View similar to Fig. 3, showing the position of the valve when the piston-head is at the extreme left end of its stroke. Fig. 5 is a view similar to Figli, showing the position of the valves when the piston is a little past its center toward the left, and Fig. 6 is a similar view showing the position of the valves when the piston is a little past the center toward the right. Figs. 7 and 8 represent perspective views of the two valves reversed.

In Figs. 2, 4, 5, and 6 small arrows are shown to indicate the direction in which the piston is traveling.

A represents the cylinder, B the pistonhead, B2 the piston-rod, a a2 the steam-ports, a3 the exhaust-port, and O the steam-chest, all formed and arranged as in an ordinary slidevalve steam-engine.

I have not shown the slides, cross-head, connecting-rod, engine-frame, &c., as their coned to be moved back and forth by a stem, F,

connecting it with theeccentrics E on the main driving-shaft D. (See Fig. 1.) The slidevalve F differs from an ordinary slide-valve by being provided with side ports, e e2, oneonV each side of the exhaust-port d, and with a central port, e3, leading from the exhaust-cavity d back through the body of the valve between the ports e e2, as shown. The back of the valve F is provided with a steam-tight face, and upon this back face another valve,` F2, is adapted to be vibrated by a stem, G, connecting it with the second eccentric, E2, on the shaft D. eccentric E2 is a little greater than the throw of the eccentric E. In an engine of ten-inch bore and twenty-inch stroke thisdifference is about one-half an inch, but may be varied to suit circumstances. The valve F2 is provided with a cavity, g, in its under side, wide enough to cover the ports e e3 or e2 e3, but not wide enough to cover all three of the ports e e2 es at once. p

After an engine exhaust-s, the exhaust end of the cylinder is lled with heated air and steam under a pressure equal to or slightly in excess of the atmosphere, and when the slide-valve F is moved over to cut off the steam on the steam end of the cylinder it also cuts off the exhaust or closes the connection between the exhaustport a? and the steam-port a or a2, (which for the time being happens to be at the exhaust end of the cylinder,) leaving the exhaust end of the cylinder full of air and without means of escape, which air the piston-head in the completion of its stroke compresses very suddenl y, forming what is known as back-pressure, which greatly retards the engine and requires a greater pressure of steam on the other side of the piston to move it than would be required if this back-pressure were not present.

To form a means of escape for the air in the (See Fig. l.) The throw of the.

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exhaust end of the cylinder, and to prevent the possibility of the formation of back-pressure therein, is the function of the supplemental valve F2 and the ports e e2 e3 in the valve F.

This action is clearly illustrated by the different figures of the drawings.

In Fig. 2 the valve F is shown just opening to admit steam to the right hand end of the cylinder, while the exhaust-port a3 is open, the

1o valve F2 and its ports e e2 c3 at this point being inactive, as will be readily seen.

In Fig. 4the relative positions of the valves are shown in the reverse position, represent ing their positions at opposite points of the i5 stroke from that shown in Fig. 3.

In Fig. 5 the valve F is shown after it has been moved far enough to cut ofi' the steam to utilize its expansive power, which movement in anordinary valve also cuts ott' the exhaust 2o escape; but in my arrangement the movement of the valve F brings the port e above the port a', and the eccentric F. will move the valve F2 so that its cavity tr/will connect the ports e and e3, and thus open communication with the outer air through the ports a', e', e3, d, and a3, or, in other words, prevent thek cut- Ling off of the exhaust-ports a3 from the exhaust end of the cylinder.

Fig. 6 shows the arrangement of the valves 3o at the opposite point of the stroke from that shown in Fig. 5, both ends of both valves being the same except for the slight differences the lap77 and lead 7 of the valves may render necessary.

By this simple device I entirely prevent the accumulation of confined air in the exhaust end ofthe cylinder, leaving the piston free to move without resistance, and am consequently enabled to utilize to a much greater extent the expansive force of the steam, as an engine 4o provided with this relief-valve F2 can be set to cut off at an earlier moment of its stroke than an engine provided with the ordinary valve only.

Having thus described my invention, what I claim as new is- In a steam-engine, a cylinder having the steam-ports a ce2, exhaust-port a3, and piston B', a valve, F', having exhaust-cavity d, side ports, c e?, and central port, e3, and adapted 5o to be moved back and forth to alternately open and close said steam and exhaust ports, and a relief-valve, F2, having cavity g and adapted to be moved back and forth over said valve F to connect its cavity g alternately with said ports e c3 and e2 e3, whereby communication is opened between said exhanstport a3 and the exhaust end of said cylinder to prevent the formation of back'pressure therein.

In testimony whereof I have hereunto set 6o my hand in the presence of two subscribing witnesses.

JAMES HENRY DUFFEY.

Vitnesses:

C. N. WooDwAnD, H. S. WEBsTER. 

